System.Diagnostics.Process prKeyBoard = System.Diagnostics.Process.Start("osk.exe");
            if (saveFile.ShowDialog() == DialogResult.OK)
            {
                //  ...

                // 关闭屏幕键盘
                if (prKeyBoard != null)
                {
                    prKeyBoard.CloseMainWindow();
                    /// prKeyBoard.Close();
                }
            }

/// <summary>
        /// 检查MDI子窗体是否存在
        /// </summary>
        /// <param name="mdiChildTypeString"></param>
        /// <returns></returns>        
        private bool IsMDIChildFormExist(string mdiChildTypeString)
        {
            Form currentMDIChild = null;
            foreach (Form mdiChildFrm in this.MdiChildren)
            {
                if (mdiChildFrm.GetType().ToString() == mdiChildTypeString)
                {
                    currentMDIChild = mdiChildFrm;
                    break;
                }
            }

            if (currentMDIChild != null)
            {
                if (currentMDIChild.WindowState == FormWindowState.Minimized)
                {
                    currentMDIChild.WindowState = FormWindowState.Normal;
                }
                currentMDIChild.TopMost = true;
                currentMDIChild.Activate();
                currentMDIChild.Focus();
                return true;
            }
            else
            {
                return false;
            }

        }